Current measurement signal device with electrical isolation, electronic trip unit, and circuit breaker comprising one such device

ABSTRACT

The current measurement device with electrical isolation comprises an input signal connected to an electrical shunt, an output of an output signal, and signal transfer means with electrical isolation receiving the input signal and supplying said output signal. The transfer means comprise at least one signal transformer having at least one primary winding to receive a primary signal representative of said input signal, switching means to switch the input signal and supply the latter to said primary winding, and electrically isolated control means of the switching means comprising a control input receiving control signals during switching periods. A trip unit and an electrical circuit breaker comprises one such current measurement device and a processing unit processing electrical protection functions.

This application is a national stage entry of International ApplicationNo. PCT/FR2007/002025, filed Dec. 10, 2007 designating the U.S., whichclaims the benefit of French Application No. 06 11008, filed Dec. 18,2006.

BACKGROUND OF THE INVENTION

The invention relates to a current measurement device with electricalisolation comprising:

-   at least one electrical shunt designed to have a current to be    measured flow through the latter,-   at least one input signal input connected to said shunt to receive a    signal representative of a current,-   an output of an output signal representative of said input signal    representative of a current, and-   signal transfer means with electrical isolation receiving the input    signal and supplying said output signal,    said transfer means comprising:-   at least one signal transformer having at least one primary winding    to receive a primary signal representative of said input signal,-   switching means to switch the input signal and provide said primary    signal representative of said input signal to said primary winding,    and-   control means of the switching means comprising a control signal    input receiving control signals during switching periods, and an    output electrically isolated from the control signal input and    connected to said switching means to command primary signal    switching during said switching periods.

The invention also relates to an electronic trip unit and a circuitbreaker comprising one such current measurement device.

STATE OF THE ART

Known current measurement devices with electrical isolation aregenerally achieved with current transformers. But when the current to bemeasured is either AC or DC, coupling devices connected to shunts can beused. Such known coupling devices with electrical isolation aregenerally achieved with a first part 1 for processing an input signal SIand a second part 2 for processing an output signal SO. A diagram of aknown device is represented in FIG. 1. A first input signal part 1generally comprises a signal amplifier 3 and a modulator 4 to transfer atransformed value or a digital value of the input signal. The modulator4 is generally connected to a transformer 5 or to other couplers toisolate the first part 1 from the second signal processing part 2. Inthe second part 2, the signal is processed and reconditioned in acircuit 6 to be processed as output signal SO. In devices of the priorart, the first part 1 receiving the input signal requires an electricpower supply circuit 7 for the amplifier and modulator to be able towork. In the prior-art layout, a first main electric power supply 8supplies the output signal processing circuit 6 and an electric powerconversion circuit comprising a chopper 9 and a power supply transformer10 and the circuit 7 to supply electric power to the whole of first part1.

In other layouts there can be two independent power supplies to supplythe first part and the second part separately.

Known state-of-the-art measurement current measurement devices withelectrical isolation requiring auxiliary power supply circuits aredifficult to integrate in measurement processing circuits or equipmentunits of small dimensions. Moreover, such devices also have the drawbackof consuming electric power thereby making them incompatible with verylow-consumption applications. In particular, they cannot be easilyintegrated in modular electrical circuit breakers.

Certain devices comprise transformers receiving a switched currentmeasurement signal as represented in the documents GB1585889 andUS2003/0076086. However, in the document US2003/0076086 the signalswitch control means are opto-electronic components that areincompatible with industrial applications having large thermal stresses.In particular, these components have efficiency and speedcharacteristics that decrease very greatly when the temperatureincreases. These high operating temperatures are particularly present inelectrical equipment such as electronic trip devices and electricalcircuit breakers.

SUMMARY OF THE INVENTION

The object of the invention is to provide a current measurement devicewith electrical isolation that does not require power supply of the partprocessing the input signal and that is able to operate normally withvery large temperature swings, as well an electronic trip unit and acircuit breaker comprising one such device.

In a current measurement device with electrical isolation according tothe invention, said control means of the switching means comprisecoupling means by electromagnetic induction and/or by capacitiveconnection.

Said signal transformer comprises an output winding connected todetection means receiving a switched secondary output signal andsupplying an output signal representative of the input signal.

In a first alternative embodiment, input signal switching isunidirectional. In a second alternative embodiment, input signalswitching is bidirectional or with reversal.

In a first particular embodiment, the signal transformer comprises twoprimary windings connected with opposite winding directions, a first endof each winding is connected to a common point of the windings toreceive the signal input, and second ends of the windings are connectedto first switching means and to second switching means connected to asecond end of said shunt to switch and direct the input signalalternately onto the first and second winding.

The switching means preferably switch input signals onto the primarywindings with command overlap at the start and end of switching.

In a second particular embodiment, the signal transformer comprises aprimary winding connected to switching means comprising four electronicswitches connected in the form of a bridge with two branches, externallines of the bridge connected to said shunt to receive the input signaland internal branches of the bridge being connected to said primarywinding of said signal transformer, said switches in the form of abridge being commanded alternately in crossover manner to reverse thedirection of the primary signal applied to the primary winding of saidsignal transformer.

In a third particular embodiment, the input signal is applied to a shuntformed by a bridge of two measuring resistors connected in series, acommon point of the measuring resistors being connected to a first endof a primary winding of the signal transformer, a second end of saidprimary winding of the signal transformer being connected to a commoncentral part of a switching bridge with two switches of the switchingmeans, external lines of the switches of said bridge being connected tothe external parts opposite the common point of the resistor bridge, thetwo switches operating alternately to reverse the direction of theprimary signal applied to the primary winding of said signaltransformer.

The detection means preferably comprise means for filtering the switchedoutput signal.

In a preferred embodiment, the detection means comprise synchronousdetection means synchronized with control of the switching means toreconstitute an output signal representative of said input signal.

Advantageously, the signal transformer comprises:

-   at least a first primary winding to receive a first input signal    representative of a current flowing in a first shunt and at least    first switching means to switch said first input signal,-   at least a second primary winding to receive a second input signal    representative of a current flowing in a second shunt and at least    second switching means to switch said second input signal, sais    second shunt being electrically separated from said first shunt, and-   at least one secondary winding to supply a signal representative of    said first input signal or of said second input signal.

Advantageously, the current measurement device comprises processingmeans:

-   to select first control means of said first switching means to    supply an output signal representative of said first input signal,    or-   to select second control means of said second switching means to    supply an output signal representative of said second input signal.

Preferably, the processing means command selection of the control meanssequentially to supply a multiplexed output signal sequentiallyrepresentative of each input signal.

Advantageously, the processing means command control meanssimultaneously to supply an output signal representative of the sum ofthe input signals.

Preferably, the processing means comprise signal sampling means tosample an output signal representative of a multiplexed secondary signaland to supply values representative of each input signal, sampling beingsynchronized with selection of the control means.

Preferably, sampling is performed after a preset time delay followingthe start of a control impulse closing the switching means.

Preferably, the processing means activate command of the control meansduring periods of short duration and stop command of the control meansduring periods of long duration.

In a preferred embodiment, said control means of the switching meanscomprise at least one control transformer having a primary windingreceiving the control signals and a secondary winding to controlswitching means.

Preferably, at least one control transformer of the control means is anair-insulated transformer having a primary winding on a first face of acircuit support and a secondary winding on a second face of said circuitsupport.

Preferably, the circuit support is composed of a polyimide material.Advantageously, the circuit support has a thickness comprised between 3and 80 μm.

In another embodiment, the measuring transformer is an air-insulatedtransformer having at least one primary winding on a first face of acircuit support and a secondary winding on a second face of said circuitsupport.

Advantageously, the circuit support is composed of a polyimide materialand has a thickness comprised between 3 and 80 μm.

In another embodiment, said at least one control transformer and atleast one measuring transformer are placed on the same insulatingsupport with windings on each side of said circuit support.

Advantageously, the circuit support is composed of a polyimide materialand has a thickness comprised between 3 and 80 μm.

In another embodiment, said control means of the switching meanscomprise at least two capacitive coupling capacitors each having a firstelectrode to receive the control signals and a second electrode tocommand switching means.

Advantageously, a circuit support being composed of a polyimide materialand having a thickness comprised between 3 and 80 μm, said circuitsupport has the first electrodes of said two coupling capacitors on afirst face and the second electrodes of said two coupling capacitors onthe second face.

In another embodiment, the measuring device comprises control means ofthe switching means and the switching means are grouped in anelectromagnetic microcomponent of MEMS type.

An electronic trip unit according to the invention comprising:

-   a current measurement device,-   a processing unit for processing protection functions connected to    the current measurement device to receive at least one signal    representative of a current,-   a trip output to supply a trip signal according to said at least one    current signal, comprises at least the current measurement device    defined above comprising at least one electrical shunt for flow of a    current to be measured, the current signal supplied to the    processing unit being processed by the protection functions to    supply a trip signal.

An electrical circuit breaker according to the invention comprising:

-   electric power contacts,-   an operating mechanism commanding opening of said electric contacts,-   a current measurement device connected in series with said electric    contacts,-   a processing unit for processing protection functions connected to    the current measurement device to receive at least one signal    representative of a current,-   a trip output to supply a trip signal of opening of the electric    contacts according to said at least one current signal,    comprises at least the current measurement device defined above    comprising:—at least one electrical shunt for flow of a current to    be measured, the current signal supplied to the processing unit    being processed by the protection functions to supply said trip    signal of opening of the electric contacts.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become more clearly apparent from thefollowing description of particular embodiments of the invention, givenas non-restrictive examples only and represented in the accompanyingdrawings in which:

FIG. 1 represents a diagram of a current measurement device withelectrical isolation according to the state of the art;

FIG. 2 represents a diagram of a current measurement device according toa first embodiment of the invention;

FIG. 3 represents a diagram of a device according to FIG. 2 withswitching control by transistors;

FIG. 4 represents a first diagram of a current measurement deviceaccording to an embodiment of the invention of switching with reversaltype;

FIGS. 5A to 5G represent timing charts of signals in a device accordingto the embodiment of FIG. 4;

FIGS. 6 and 7 represent alternative embodiments of current measurementdevices according to embodiments of the invention of switching withreversal type;

FIGS. 8A to 8C represent plots of signals in current measurement devicesaccording to embodiments of the invention with bidirectional switching;

FIG. 9 represents an embodiment of a current measurement deviceaccording to an embodiment of the invention of the diagram of FIG. 7;

FIG. 10 represents a first diagram of a current measurement deviceaccording to an embodiment of the invention with input signalmultiplexing on a common signal transformer;

FIG. 11 represents a second diagram of a current measurement deviceaccording to an embodiment of the invention with input signalmultiplexing on a common signal transformer;

FIGS. 12A to 12G represent plots of signals in a device of FIG. 11;

FIG. 13 represents a flowchart showing a measurement sample acquisitioncycle;

FIG. 14 represents a diagram of an electrical equipment unit comprisinga measuring device according to an embodiment of the invention;

FIG. 15 represents an impulse transformer in printed form used in thecontrol means of a current measurement device according to an embodimentof the invention;

FIG. 16 represents a grouping of impulse transformers and measuringtransformers in printed form used in a current measurement deviceaccording to an embodiment of the invention;

FIGS. 17 and 18 show alternative embodiments of devices according toembodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 2 represents a diagram of a current measurement device according toa first embodiment of the invention. The current measurement device withelectrical isolation comprises at least one input 11 of an input signalSI connected to an electrical shunt 40 for measuring a current IP. Thedevice also comprises an output 12 of an output signal SO representativeof said input signal, and signal transfer means 13 with electricalisolation receiving the input signal and supplying said output signal.The transfer means comprise at least one signal transformer 14 having atleast one primary winding 15 to receive a primary signal SPrepresentative of said input signal SI. The input signal is switched byswitching means 16 represented by a controlled switch to supply saidprimary signal SP representative of said input signal SI to said primarywinding 15. Switching means 16 are commanded by control means 17comprising a control signal input 18 receiving control signals SC. Anoutput 20 of the control means is electrically isolated from controlsignal input 18 and is connected to said switching means 16 to commandprimary signal switching at a switching frequency.

In FIG. 2 the signal SI is switched by electronic switch 16 at a highswitching frequency to supply a switched signal SP on primary winding 15of signal transformer 14. Said signal transformer 14 comprises an outputwinding 21 connected to detection means 23 receiving a switchedsecondary output signal SD and supplying an output signal SOrepresentative of input signal SI. The secondary signal SD induced in asecondary winding 21 of the signal transformer is then processed tosupply output signal SO. Processing can comprise amplification in anamplifier 22 followed by detection and filtering in an output signalprocessing module 23. Detection can be performed by single-alternationrectifying, by envelope detection or by synchronous rectifying.

Control signal SC of the switching means is preferably provided by aswitching signal generator 24 located in second signal processing part2. Processing module 23 and control signal generator 24 are preferablylocated in the same processing unit 25 and are supplied by the samepower supply circuit 26. This power supply circuit 26 can also supplyamplifier 22. The control signals are applied to an impulse transformer27 of the isolated control means. The output of the control means cancomprise a signal conditioning circuit 28 comprising for example a diode29 and a capacitor 30 to be adapted to switching means 16.

FIG. 3 shows a layout diagram of a device according to an embodiment ofthe invention with switching control with field-effect transistors 31having reverse-connected internal diodes 32. These transistors areconnected in series in reverse direction, i.e. their sources areconnected together and act as reference for the control signals suppliedby impulse transformer 27, and their control electrodes are connectedtogether to receive said control signals of the transformer 27 viaconditioner 28. Whatever the direction or the polarity of the inputsignal, the two transistors are turned on. If no control signal issupplied, both the transistors are turned off, and depending on thedirection or the polarity of the input signal, only one of the twodiodes blocks the input signal. With such a layout, the device operateswhatever the polarity and the level of the input signal which can be ACor DC. In the diagram of FIG. 3, a measuring or load resistor 40 isconnected on input of the device to generate input signal SI. Ifresistor 40 is an electrical shunt, signal SI is a current measurementsignal.

If the input signal has a very low voltage, less than 0.6 volts forexample, a single field-effect transistor 31 can be sufficient. In thiszone, the transistor operates bidirectionally and the associated diodeis not turned-on in forward bias.

For current measurement, the input impedance of signal transformer 14 ispreferably very low. Primary winding 15 then comprises a small number ofturns.

The current measurement device can operate in switching mode of theunidirectional input signal by switching the input signal in the samepolarity on consecutive control orders and applying it also with thesame polarity to the primary winding of the signal transformer.

To improve operation of signal transformer 14, switching of the inputsignal can advantageously be bidirectional. In this case, the inputsignal is switched and reversed at each command order to supply aprimary signal having reverse consecutive induction directions on aprimary induction circuit of signal transformer 14. Thus, a magneticcoupling circuit of the signal transformer is magnetized in onedirection and then demagnetized and re-magnetized in another directionaccording to the control orders to control the remanence of saidmagnetic circuit and improve the efficiency of signal transfer betweenthe primary and secondary of transformer 14.

FIG. 4 represents a first diagram of a current measurement deviceaccording to an embodiment of the invention with bidirectionalswitching. In this case, signal transformer 14 comprises two primarywindings 15A and 15B connected with reverse winding directions, a firstend of each winding is connected to a common point of the windings toreceive the input signal input, second winding ends are connected tofirst switching means 16A and to second switching means 16B to switchand direct input signal SI alternately onto the first and secondwinding. Preferably, to improve operation of the magnetic circuit oftransformer 14, the switching means switch the signals onto the primarywindings with a command overlap at the start and end of switching.Signal generator 24 supplies the control signals of switching means 16Aand 16B represented by controlled switches. Generator 24 also supplies afirst synchronization signal SY to processing module 23 to performsynchronous detection of the output signal. Depending on the directionof the signal on the primary, the output signal can in fact be positiveor negative. Synchronous detection enables a signal polarityrepresentative of the input signal polarity to be had. Generator 24 canalso supply or receive a second synchronization signal to operate with asignal sampler. The generator, synchronous detector, and sampler canform part of the same circuit.

FIGS. 5A to 5G represent timing charts of signals in a currentmeasurement device according to the embodiment of FIG. 4. In FIG. 5A, aplot 41 shows an input signal SI. In this figure, input signal SI is DCand of positive polarity. FIG. 5B shows a plot 42 representative ofcontrol of switching means switch 16A. FIG. 5C shows a plot 43representative of control of switching means switch 16B. FIG. 5D shows aplot 44 representative of a current I15A in first primary winding 15A ofsignal transformer 14. FIG. 5E shows a plot 45 representative of acurrent I15B in second primary winding 15B of signal transformer 14.FIG. 5F shows a plot 46 representative of a current resultant I15corresponding to currents I15A and I15B flowing in the two primarywindings 15A and 15B of signal transformer 14 controlled with directionreversal. FIG. 5G shows a plot 47 representative of an output signal SDon secondary winding 21 of signal transformer 14.

At a time t1, closing of switch 16A is commanded whereas switch 16B hasjust opened. Winding 15A receives input signal SI. It generates acurrent I15A and an increasing magnetic induction I15. This inductiongenerates an output signal on the transformer secondary 21 that is equalto the derivative of the flux, therefore a positive signal SD. At a timet2, closing of switch 16B is commanded whereas opening of switch 16A iscommanded. A current I15B flows in winding 15B. Current I15A iscancelled out. The resulting magnetic induction represented by I15decreases because winding 15B is coiled in the opposite direction fromwinding 15A. Signal SD on the transformer secondary becomes negative.The alternating switchings of switches 16A and 16B induce a magneticinduction without any discontinuity in transformer 14 and therebygenerate an AC signal SD with a zero DC component.

With such a device, the induction currents in the primary are neverinterrupted and the disturbances due to switchings in the primarywindings are not induced in the secondary output signal SD. The outputsignal SD can be rectified to supply a signal of the same sign as theprimary signal. A switching period TC can be defined between the startof turn-on and end of turn-on of a switch 16, for example between timest1 and t2.

FIG. 6 represents a second diagram of a current measurement deviceaccording to an embodiment of the invention with bidirectionalswitching. In this case, signal transformer 14 comprises a primarywinding 15 connected to switching means 16 comprising four electronicswitches 16A1, 16A2 and 16B1, 16B2 connected in the form of a bridgewith two branches 50 and 51. In this layout, external lines of thebridge receive input signal SI and internal parts 53 of the branches ofthe bridge are connected to said primary winding 15 of signaltransformer 14. Said switches 16A1, 16A2 and 16B1, 16B2 in the form of abridge are commanded alternately in crossover manner to reverse thedirection of primary signal SP applied to primary winding 15 of saidsignal transformer 14. Cross-connected switches 16A1 and 16A2 arecommanded at the same time to apply the input signal in a firstdirection and cross-connected switches 16B1 and 16B2 are commanded atthe same time to apply the input signal in a second direction. Resistor40 can be a measuring resistor or an electrical shunt for measuringcurrent signals.

FIG. 7 represents a third diagram of a current measurement deviceaccording to an embodiment of the invention with bidirectionalswitching. In this case, input signal SI is applied to a bridge of twomeasuring resistors 40A and 40B connected in series. A common point 54of the measuring resistors is connected to a first end of a primarywinding 15 of signal transformer 14, and a second end of said primarywinding of the transformer signal is connected to a common central part55 of a switching bridge 56 with two switches 16A and 16B of theswitching means. External lines 57 and 58 of the switches of said bridgeare connected on external parts 59 and 60 opposite common point 54 ofthe resistor bridge. The two switches 16A and 16B operate alternately toreverse the direction of primary signal SP applied to primary winding 15of said signal transformer 14. When switch 16A is closed and switch 16Bis open, a part SIA of signal SI flowing in resistor 40A and having afirst sign, for example positive, is applied to winding 15. Then, on asubsequent switching command, switch 16B is closed and switch 16A isopen. In this case, a part SIB of signal SI present on measuringresistor 40B and having a second negative sign opposite to the firstsign is applied to transformer primary winding 15. The signal onresistor 40B is of opposite polarity to the signal on resistor 40A asthe signal reference is on common point 54.

FIGS. 8A to 8C represent plots of signals in current measurement devicesaccording to embodiments of the invention with bidirectional switching.In FIG. 8A, a plot 65 shows an AC input signal SI of sine wave form. InFIG. 8B, a plot 66 shows a signal SD supplied on a secondary of a signaltransformer having bidirectional primary signal SP control. In FIG. 8C,a plot 67 shows an output signal SO processed so as to reconstitute asine-wave signal representative of the input signal. The processingmeans detect the bidirectional signal by rectifying the signal insynchronized manner, for example with bridges of electronic switches orelectronic circuits with programmed sampling and processing. Thedetection means thus comprise means for filtering the switched outputsignal and/or synchronous detection means synchronized with control ofthe switching means to reconstitute an output signal representative ofsaid input signal.

To limit the electrical consumption of the device, processing means 25can activate command of the control means during periods of shortduration and stop command of the control means during longer periods ofinactivity. For example, in the diagram of FIG. 6, cross-connectedswitches 16A1 and 16A2 are commanded during a first period, then duringa second period, switches 16B1 and 16B2 are commanded whereas switches16A1 and 16A2 are shut down. Finally, for all the switches, control isstopped during a third period. Preferably, the first and second periodsare shorter than the third period. The periods can be regular in apreset cycle or duty cycle or be commanded randomly according to therequirements of the processing means.

FIG. 9 represents an embodiment of a current measurement deviceaccording to an embodiment of the invention of the diagram of FIG. 7. Inthis embodiment, measuring resistor 40 is an electrical shunt formeasuring the electric current. Output signal SO is then representativeof an electric current flowing in said shunt. The shunt comprises amid-point 54 separating a first part 40A and a second part 40B on eachside of the mid-point. The shunt comprises power connection pads for themeasurement to flow and three measurement connections. A commonconnection 72 is connected to point 54 of the shunt, a first externalconnection 73 is connected to the same side as first part 40A and asecond external connection 74 is connected to the same side as secondpart 40B. The switching means such as electronic switches 16A and 16Band other annexed components such as conditioning circuits 28 arearranged on a first printed circuit 80 at the electrical potential of acircuit to be measured. This circuit 80 receives the connections withthe shunt and connections with the primary of signal transformer 14 andconnections with impulse transformers 27A and 27B of control means 17. Asecond printed circuit 81 supports circuits of processing unit 25 suchas detection and processing circuits 23 and control signal generators24. The electronic circuits on printed circuit 81 are at a differentpotential and are electrically and galvanically switched with respect tothe electronic circuits located on printed circuit 80. Printed circuit81 has connections on one side with signal transformer 14 and impulsetransformers 27A and 27B and connections on another side with an input Pof power supply 82, an output 83 of signal SO and a common ground 0Vinput 84.

For measuring several voltage or current signals, several devices asdescribed above can be used in parallel. However, in particularembodiments of the invention, the signal transformer forms part of amultiplexing unit.

FIG. 10 represents a first diagram of a current measurement deviceaccording to an embodiment of the invention with input signalmultiplexing on a common signal transformer 14. Signal transformer 14comprises: at least a first primary winding 151 to receive a first inputsignal SI1 and at least first switching means 161 to switch said firstinput signal SI1, and at least a second primary winding 152 to receive asecond input signal SI2 and at least second switching means 162 toswitch said second input signal SI2, and at least one secondary winding21 to supply a secondary signal SD representative of said first inputsignal SI1 or of said second input signal SI2.

A processing unit 25 selects first control means 271 of said firstswitching means 161 to supply an output signal SO representative of saidfirst input signal SI1, or selects second control means 272 of secondswitching means 162 to supply an output signal SO representative of saidsecond input signal SI2. Thus, on signal SD of secondary winding 21 ofthe signal transformer, there can be either a signal representative ofthe first input signal or a signal representative of the second inputsignal, or a signal representative of a combination of the input signalsaccording to control of the switches of the switching means.

FIG. 11 represents a second diagram of a current measurement deviceaccording to an embodiment of the invention with multiplexing of inputsignals SI1, SI2, SI3, SI4 on a common signal transformer 14. The foursignals SI1 to SI4 can be generated on measuring resistors 401, 402, 403or 404 and then switched by switching means respectively 161, 162, 163,and 164 and controlled by impulse transformers of the control meansrespectively 271, 272, 273 and 274. In the diagram, switching means 274are completely represented in one part only whereas the others arerepresented by blocks in two parts to alleviate the diagram. Switchingof the input signals enables primary signals SP1, SP2, SP3 and SP4 to besupplied to primary windings 151, 152, 153 and 154 of signal transformer14. Galvanic or electrical isolation is represented by a broken line 86.Secondary signal SD is applied to an amplifier 22 having adjustableamplification parameters. The output signal from the amplifier isfiltered by a low-pass filter 87 before being applied to processing unit25. Processing unit 25 comprises a signal sampler 88 to sample a signalrepresentative of a multiplexed secondary signal and to supply valuesrepresentative of each input signal, sampling being synchronized withselection of the control means. Amplifier 22 and sampler 88 arereferenced by a reference circuit 89. A microcontroller or amicroprocessor located in the processing unit enables control signals ofthe switching means to be supplied and performs synchronization of thesampling for synchronous detection purposes. Microprocessor 90 receivingthe samples of signal SD separates the different values into severaloutput signals SO1, SO2, SO3 and SO4 each respectively representative ofinput signals SI1, SI2, SI3 and SI4.

The processing means preferably command selection of the control meanssequentially to supply a multiplexed output signal SO sequentiallyrepresentative of each input signal SI1 to SI4. Advantageously, theprocessing means can command control means simultaneously to supply anoutput signal SO representative of the sum of the input signals.

With a layout such as the one in the diagram of FIG. 11, the currentmeasurement device can be an electronic trip unit used in a four-polecircuit breaker receiving signals representative of signals from threephases and a neutral conductor. Measuring resistors 401, 402, 403 or 404are then current measurement shunts. In case of earth protection,simultaneous control of the four channels can supply a signal SOrepresentative of a differential current.

In another embodiment, simultaneous digital processing of the fourchannels by a processor can supply a signal SO representative of adifferential current or of the sum of the input signals.

FIGS. 12A to 12G represent plots of signals in a device of FIG. 11.States of the different switching means 161 to 164 are represented onplots 91 to 94 of FIG. 12A. State 1 corresponds to a closed state of thecorresponding switch and state 0 corresponds to open state. FIG. 12Bshows a plot 95 representative of an example of input signal SI1. FIG.12C shows a plot 96 representative of an example of input signal SI2.FIG. 12D shows a plot 97 representative of an example of input signalSI3. FIG. 12E shows a plot 98 representative of an example of inputsignal SI4. FIG. 12F shows a plot 99 representative of an example ofsignal secondary SD. FIG. 12G shows sampling of the signal secondary toseparate signal SD into four output signals SO1, SO2, SO3 and SO4representative of the four output signals SI1, SI2, SI3, and SI4.

At a time t1, switch 161 is closed and secondary signal SD becomesrepresentative of input signal SI1. After a time delay D enablingoperation of transformer 14 to be stabilized, at a time t2, signal SD issampled to have an output signal SO1 representative of signal SI1. Atthe end of control of switch 161, at a time t3, there is no longer anysignal on the transformer primary, and the secondary signal goes to azero value. At a time t4, switch 162 is closed and secondary signal SDbecomes representative of input signal SI2. After a time delay D foroperation of transformer 14 to be stabilized, at a time t5, signal SD issampled to have an output signal SO2 representative of signal SI2. At atime t6, control of switch 162 is terminated. Then, at a time t7, switch163 is closed and secondary signal SD becomes representative of inputsignal SI3. After a time delay D for operation of transformer 14 to bestabilized, at a time t8, signal SD is sampled to have an output signalSO3 representative of signal SI3. At a time t9, control of switch 163 isterminated. Finally, at a time t10, switch 164 is closed and secondarysignal SD becomes representative of input signal SI4. After a time delayD for operation of transformer 14 to be stabilized, at a time t11,signal SD is sampled to have an output signal SO4 representative ofsignal SI4. At a time t12, control of switch 164 is terminated. At atime t13, the cycle restarts by closing switch 161 and sampling SD attime t14 to provide SO1. Time delay D corresponds to the wait timebetween start of closing of the switches and sampling of secondarysignal SD on output from signal transformer 14.

FIG. 13 represents a flowchart showing a measurement sample acquisitioncycle. In a step 100, the processing unit selects the channel to bemeasured. Then, in a step 101, an electronic switch of the switchingmeans is closed. Then, after a time delay D for operation of thetransformer to be stabilized avoiding in particular parasiticoscillations in a step 102, the processing unit commands sampling of asignal representative of secondary signal SD in a step 103. Sampling isthus performed after a preset time delay D following the start of acontrol impulse closing the switching means.

FIG. 14 represents a diagram of an electrical circuit breaker with anelectronic trip unit comprising a measuring device according to anembodiment of the invention. Such an electrical circuit breaker 104comprises at least one measuring resistor 401 and 402, electric powercontacts 105 connected in series with said at least one measuringresistor, an operating mechanism 106 controlling opening of electricalcontacts 105, and processing means 107 for processing protectionfunctions commanding a relay 108 connected to said mechanism 106.According to an embodiment of the invention, the circuit breakercomprises a current measurement device 110 as described above having atleast one signal input connected to said at least one measuringresistor, and a signal output connected to protection functionprocessing means 107 to supply an output signal SO representative of acurrent flowing in said measuring resistor. In FIG. 14, there are twomeasuring resistors 401 and 402 in which two primary currents IP1 andIP2 can flow and generate input measurement signals SI1 and SI2. In thiscase, current measurement device 110 can be the same as that of FIG. 10with signal multiplexing. Resistors 401 and 402 can be resistors of verylow values such as electrical shunts.

In the embodiments described above, the control means of the switchingmeans are preferably impulse transformers 27, 271, 272 having a primarywinding 115 receiving the control signals and a secondary winding 116 tocommand switching means.

When the control means of the switching means are impulse orhigh-frequency control transformers, the natural operating frequency canbe very high to reduce the size of or to eliminate the magnetic circuit.Control can take the form of bursts of signals at very high frequencyduring a control period. FIG. 15 represents an impulse transformer inprinted form used in the control means of a current measurement deviceaccording to an embodiment of the invention. In this case, the impulsetransformer is an air-insulated transformer having a primary winding 115on a first face 117 of a printed circuit 118 and a secondary winding 116on a second face 119 of said printed circuit. The operating frequency isthen very high to achieve very small winding sizes. In the embodiment ofFIG. 15, each winding has thirteen turns with an outside dimension ofless than one centimetre per side. Naturally in these cases theoperating frequency of the control means is much higher than theswitching frequency. The control signals are then square wave pulses orbursts of impulses at high frequency supplied during switching periodsTC. The printed circuit can also be an etched circuit or any othercircuit acting as support for example a ceramic or alumina support. Evenin printed form, the control transformers can have a magnetic circuitadapted to the shapes and dimensions of the circuit support. In order toreduce the sizes of said air-insulated control transformer, a circuitsupport 118 is advantageously composed of a polyimide material. Thecircuit support preferably has a thickness E comprised between 3 and 80μm.

In a particular embodiment case, the measuring transformer can be anair-insulated transformer having at least one primary winding 15 on afirst face of a circuit support 118 and a secondary winding 21 on asecond face of said circuit support. The circuit support isadvantageously composed of a polyimide material with a thickness Ecomprised between 3 and 80 μm.

FIG. 16 shows an assembly of two control transformers and a measuringtransformer placed on the same insulating support with windings on eachside of said circuit support. In this case as well, the circuit supportis advantageously composed of a polyimide material having a thickness Ecomprised between 3 and 80 μm.

FIGS. 17 and 18 show alternative embodiments of devices according toembodiments of the invention.

In FIG. 17, the control means of the switching means are a doublecapacitive connection 120 letting the impulses pass and blocking the DCor low frequency current to achieve galvanic isolation. On each branchof the capacitive connection, the control signals are complementary tomake a control current flow between the two connections and guaranteecommon mode electrical insulation. Said control means of the switchingmeans thus comprise at least two capacitive coupling capacitors 501, 502each having a first electrode 503 to receive the control signals and asecond electrode 504 to command switching means. The capacitors arepreferably achieved on a circuit support 505 composed of a polyimidematerial having a thickness comprised between 3 and 80 μm. In this case,said circuit support has first electrodes 503 of said two couplingcapacitors 501 and 502 on a first face and second electrodes 504 of saidtwo coupling capacitors 501 and 502 on the second face.

In FIG. 18, the control means of the switching means and the switchingmeans are grouped in an electromagnetic microcomponent 122 preferablyachieved by the technology referred to as MEMs.

Several types of switching means can be used, in particular field-effecttransistors, bipolar transistors, or switches with electromagnetic,electrostatic or optic control.

The switching frequency of input signal SI may depend on the size of thecoupling transformer used and on the throughput through saidtransformer. This switching frequency is advantageously linked to thecapacities of the detection and sampling means.

The current measurement devices described above enable any type ofelectric signals to be measured, in particular currents, voltages, orseveral types in multiplexed mode on the same magnetic circuit of thesignal transformer. For voltage measurement, the input signal can beprovided by a voltage divider bridge.

The electrical units in which the current measurement device isimplemented can be of any type. If the electrical unit compriseselectrical protection functions such as those of a relay or of a circuitbreaker trip unit, the measuring resistors are advantageously electricalshunts. These shunts can be of resistance or impedance type for examplewith inductance.

1. A current measurement device with electrical isolation, comprising:at least one electrical shunt (40) for permitting a current to bemeasured to flow therethrough, at least one input port for receiving aninput signal (SI), connected to said shunt for receiving a signalrepresentative of a current, an output port for outputting an outputsignal (SO) representative of said input signal representative of acurrent, and signal transfer means with electrical isolation forreceiving an input signal and supplying said output signal, saidtransfer means comprising: at least one signal transformer (14) havingat least one primary winding (15, 15A, 15B, 151, 152, 153, 154) forreceiving a primary signal (SP, SP1, SP2, SP3, SP4) representative of aninput signal (SI, SIA, SIB, SI1, SI2, SI3, SI4), switching means (16,16A, 16B, 161, 162, 163, 164, 31, 32) for switching the input signal andproviding a primary signal representative of said input signal to saidprimary winding, and control means (17, 17A, 17B, 27, 27A, 27B, 271,272, 273, 274) of the switching means, comprising a control signal input(SC) for receiving control signals during switching periods (TC), and anoutput electrically isolated from the control signal input and connectedto said switching means (16, 16A, 16B, 161, 162, 163, 164, 31, 32) forcommanding primary signal switching during said switching periods (TC),characterized in that said control means of the switching means compriseelectromagnetic induction and/or capacitive connection coupling meanscoupled to said switching means.
 2. The current measurement deviceaccording to claim 1 characterized in that said signal transformer (14)comprises an output winding (21) connected to detection means (23)receiving a switched secondary output signal (SD) and supplying anoutput signal representative (SO) of the input signal (SI, SIA, SIB,SI1, SI2, SI3, SI4).
 3. The current measurement device according toclaim 2 characterized in that the detection means (23) comprise meansfor filtering the switched output signal.
 4. The current measurementdevice according to claim 2 characterized in that the detection means(23) comprise synchronous detection means synchronized with control ofthe switching means (16, 16A, 16B, 161, 162, 163, 164, 31, 32) toreconstitute an output signal (SO) representative of said input signal(SI).
 5. The current measurement device according to claim 1characterized in that switching of the input signal (SI, SIA, SIB, SI1,SI2, SI3, SI4) is unidirectional.
 6. The current measurement deviceaccording to claim 1 characterized in that switching of the input signal(SI, SIA, SIB, SI1, SI2, SI3, SI4) is bidirectional or with reversal. 7.The current measurement device according to claim 1 characterized inthat the signal transformer (14) comprises two primary windings (15A,15B) connected with reverse winding direction, a first end of eachwinding is connected to a common point of the windings to receive thesignal input, and second ends of the windings are connected to firstswitching means (16A) and to second switching means (16B) to switch anddirect the input signal (SI, SIA, SIB) alternately onto the first andsecond winding.
 8. The current measurement device according to claim 7characterized in that the switching means switch input signals on theprimary windings (15A, 15B) with a command overlap at the start and endof switching.
 9. The current measurement device according to claim 1characterized in that the signal transformer (14) comprises a primarywinding (15) connected to switching means (16) comprising fourelectronic switches (16A1, 16A2, 16B1, 16B2) connected in the form of abridge with two branches (50, 51), external lines of the bridgereceiving the input signal (SI) and internal branches (53) of the bridgebeing connected to said primary winding (15) of said signal transformer,said switches in the form of a bridge being commanded alternately incrossover manner to reverse the direction of the primary signal (SP)applied to the primary winding (15) of said signal transformer (14). 10.The current measurement device according to claim 1 characterized inthat the input signal (SI, SIA, SIB) is applied to a shunt formed by abridge of two measuring resistors (40A, 40B) connected in series, acommon point (54) of the measuring resistors being connected to a firstend of a primary winding (15) of the signal transformer (14), a secondend of said primary winding (15) of the signal transformer beingconnected to a common central part (55) of a switching bridge with twoswitches (16A, 16B) of the switching means, external lines (57, 58) ofthe switches of said bridge being connected to the external parts (59,60) opposite the common point of the resistor bridge, the two switchesoperating alternately to reverse the direction of the primary signal(SP) applied to the primary winding (15) of said signal transformer(14).
 11. The current measurement device according to claim 1characterized in that the signal transformer (14) comprises: at least afirst primary winding (151) to receive a first input signal (SI1)representative of a current flowing in a first shunt (40C) and at leastfirst switching means (161) to switch said first input signal, at leasta second primary winding (152) to receive a second input signal (SI2)representative of a current flowing in a second shunt (40D) and at leastsecond switching means (162) to switch said second input signal, saidelectrical shunt being electrically separated from said first shunt, andat least one secondary winding (21) to supply a signal (SD)representative of said first input signal (SI1) or of said second inputsignal (SI2).
 12. The current measurement device according to claim 11further comprising processing means (25): to select first control means(271) of said first switching means (161) to supply an output signal(SO) representative of said first input signal (SI1), or to selectsecond control means (272) of said second switching means (162) tosupply an signal output (SO) representative of said second input signal(SI2).
 13. The current measurement device according to claim 12characterized in that the processing means (25) command selection of thecontrol means sequentially to supply a multiplexed output signal (SO)sequentially representative of each input signal (SI1, SI2, SI3, SI4).14. The current measurement device according to claim 12 characterizedin that the processing means (25) command control means simultaneouslyto supply an output signal (SO) representative of the sum of the inputsignals.
 15. The current measurement device according to claim 12characterized in that the processing means (25) comprise signal samplingmeans (88) to sample an output signal representative of a multiplexedsecondary signal (SD) and to supply values representatives of each inputsignal, sampling being synchronized with selection of the control means.16. The current measurement device according to claim 15 characterizedin that sampling is performed after a preset time delay (D) followingthe start of a control impulse closing switching means (16, 16A, 16B,161, 162, 163, 164, 31, 32).
 17. The current measurement deviceaccording to claim 12 characterized in that the processing means (25)activate command of the control means during periods of short durationand stop command of the control means during periods of long duration.18. The current measurement device according to claim 1 characterized inthat said control means of the switching means comprise at least onecontrol transformer (27, 271, 272, 273, 274, 27A, 27B) having a primarywinding receiving the control signals and a secondary winding to controlswitching means.
 19. The current measurement device according to claim18 characterized in that the at least one control transformer of thecontrol means is an air-insulated transformer having a primary winding(115) on a first face (117) of a circuit support (118) and a secondarywinding (116) on a second face (119) of said circuit support.
 20. Thecurrent measurement device according to claim 19 characterized in thatthe circuit support is composed of a polyimide material.
 21. The currentmeasurement device according to claim 19 characterized in that thecircuit support has a thickness (E) comprised between 3 and 80 μm. 22.The current measurement device according to claim 18 characterized inthat said at least one control transformer (371, 372) and at least onemeasuring transformer (14) are placed on the same insulating support(118) with windings (116, 116, 15, 21) on each side of said circuitsupport.
 23. The current measurement device according to claim 22characterized in that the circuit support is composed of a polyimidematerial and has a thickness (E) comprised between 3 and 80 μm.
 24. Thecurrent measurement device according to claim 1 additionally comprisinga measuring transformer which is an air-insulated transformer having atleast one primary winding (15) located on a first face (117) of acircuit support (118) and a secondary winding (21) on a second face(119) of said circuit support.
 25. The current measurement deviceaccording to claim 24 characterized in that the circuit support iscomposed of a polyimide material and has a thickness (E) comprisedbetween 3 and 80 μm.
 26. The current measurement device according toclaim 1 characterized in that said control means of the switching meanscomprise at least two capacitive coupling capacitors (501, 502) eachhaving a first electrode (503) to receive the control signals and asecond electrode (504) to command switching means.
 27. The currentmeasurement device according to claim 26 further comprising a circuitsupport (505) composed of a polyimide material having a thicknesscomprised between 3 and 80 μm, said circuit support having the firstelectrodes (503) of said two coupling capacitors (501, 502) on a firstface and the second electrodes (504) of said two coupling capacitors onthe second face.
 28. The current measurement device according to claim 1characterized in that it also comprises control means of the switchingmeans (17) and that the switching means (16) are grouped in anelectromagnetic microcomponent (122) of MEMS type.
 29. An electronictrip unit, comprising: a current measurement device, a processing unit(107) for processing protection functions, connected to the currentmeasurement device to receive at least one signal (ID) representative ofa current, trip output means for supplying a trip signal according tosaid at least one current signal, wherein said current measurementdevice is a current measurement device according to claim 1 so that thecurrent signal supplied to the processing unit is processed by theprotection functions to supply a trip signal.
 30. An electrical circuitbreaker comprising: electric power contacts (105), an operatingmechanism (106) for commanding opening of said electric contacts, acurrent measurement device according to claim 1 connected in series withsaid electric contacts, a processing unit (107) for processingprotection functions connected to the current measurement device and forreceiving at least one signal (ID) representative of a current, tripoutput means for supplying a trip signal for opening of the electriccontacts according to said at least one current signal, wherein thecurrent signal supplied to the processing unit is processed by theprotection functions to supply said trip signal for opening the electriccontacts.